Propellant burning rate catalyst and method of propulsion

ABSTRACT

1. An improved solid composite type propellant composition comprising: as a base propellant, a major amount of a solid inorganic oxidizing salt as an oxidizer component and a minor amount of a suitable binder component comprised of a material selected from the group consisting of natural rubber, synthetic rubber, copolymers of a conjugated diene containing from 4 to 10 carbon atoms per molecule with a polymerizable heterocyclic nitrogen base, copolymers of a conjugated diene containing from 4 to 10 carbon atoms per molecule with styrene asphalt, pitch, mixtures of asphalt and natural rubber, mixtures of asphalt and synthetic rubber, mixtures of pitch and natural rubber, mixtures of pitch and synthetic rubber, epoxy resins, polybutadiene, polybutene, polyisobutylene, hydrogenated polybutadiene, natural waxes, synthetic waxes, polyethylenes, polysulfide rubbers, acrylic resins, polyvinyl resins, and nitro polymers; and from about 0.25 to about 12 parts by weight per 100 parts by weight of said base propellant of a burning rate catalyst consisting essentially of a complex of a pyridine containing copper and hexavalent chromium and selected from the group of compounds characterized by the formula   D R A W I N G

urnsitle Y 7 Aug. 21, 1973 PROPELLANT BURNING RATE CATALYST AND METHODOF PROPULSION Charles 11. Burns|de,'Waco, Tex.

{ 7}] Assigncc: Phllllps Petroleum Company,

' Burtlcsville, Okla.

[22 Filed; Nov. 2, 1959 i [21] Appl. No.: 850,491

[75] Inventor:

[52] US. Cl 60/219, 149/18, 149/19,

v149/20 [51] Int. Cl. .i C06d'5/06 [58] Field of Search 60/35, 4, 219;

[56] References Cited UNITED STATES PATENTS 2,555,333 6/1951 Grand etal149/19 2,637,274 5/1953 Taylor et a1. 149/19 2,877,504 3/1959 Fox 149/192,904,420 9/1959 Halker 149/19 2,923,610 2/1960 Harper et a1 149/192,923,612 2/1960 Harrison 149/19 Primary Examiner-Benjamin R. PadgettAttorney-Young & Quigg component and a minor amount of a suitable bindercomponent comprised of a material selected from the groupconsisting ofnatural rubber, synthetic rubber, copolymers of a conjugated dienecontaining from 4 to '10 carbon atoms per molecule with a polymerizableheterocyclic nitrogen base, copolymers of a conjugated diene containingfrom 4 to 10 carbon atoms per molecule with styrene asphalt, pitch,mixtures of asphalt and natural rubber, mixtures of asphalt andsynthetic rubber, mixtures of pitch and natural rubber, mixtures ofpitch and synthetic rubber, epoxy resins, polybutadiene, polybutene,polyisobutylene, hydrogenated polybutadiene, natural waxes, syntheticwaxes, polyethylenes, polysulfide rubbers, acrylic resins, polyvinylresins, and nitro polymers; and from about 0.25 to about 12 parts by.weight per 100 parts by weight of said base propellant of a burning ratecatalyst consisting essentially of a complex of a pyridine containingcopper and hexavalent chromium and selected from the group of compoundscharacterized by the formula Cu GU01 \N/ 4-2m wherein: R is selectedfrom the group consisting of alkyl and alkenyl radicalscontaining from 1to 4 carbon atoms; R is a pyridyl radical; in is the number of R'substituents and is an integer of from 0 to l; and n is the number of Rsubstituents and is an integer of from 0 to 3.

18 Claims, No Drawings 1 PROPELLAN'I' BURNING RATE CATALYST AND METHODOF PROPULSION burning rate having a new burning rate catalystincorporated therein.

Solid propellants can be classified with respect to composition asdouble base type, single base type, and composite type. An example of adouble base propellant is ballistite which comprises essentiallynitroglycerine and nitrocellulose. Examples of single base propellantsare nitrocellulose and trinitrotoluene. Composite type propellants aregenerally composed of an oxidizer, and a binder or fuel. They maycontain other materials to improve fabrication or increase ballisticperformance such as a burning rate catalyst.

Rocket propellants have achieved considerable commercial importance aswell as military importance. Jet propulsion motors of the type in whichthe propellants of this invention are applicable can be employed to aida heavily loaded plane in take off. Said motors can also be employed asan auxiliary to the conventional power plant when an extra surge ofpower is required. Said motors can also be employed to propelprojectiles and land vehicles. Said propellants can also be used foruses other than propulsion. For example, they can be used as gasgenerators in starting devices, power units where a fluid is employed asa motive force, and other applications where a comparatively largevolume of gas is required in a relatively short period of time.

Solid propellants having relatively slow burning rates are entirelysatisfactory for use in JATO units, i.e.,

rocket units employed as jet assist take off units which aid in poweringloaded aircraft during take off. However, many of said propellantshaving relativelyslow burning rates are not entirely satisfactory foruse where a propellant having a relatively high burning rate is requiredso that maximum thrust can be developed in minimum time as in boosterrocket applications, or in said gas generator systems.

I have discovered that certain complex compounds wherein a pyridine iscomplexed with copper and hexavalent chromium, defined furtherhereinafter, are effective in increasing the burning rate of solidpropellants having relatively slow burning rates to the extent that saidpropellants can be used where propellants having high burning rates arerequired.

An object of this invention is to provide a new buming rate catalyst forsolid propellants. Another object of this invention is to provide aburning rate catalyst comprising essentially certain complexes of apyridine with copper and hexavalent chromium. Another object of thisinvention is to provide an improved propellant composition comprising abinder component, an oxidizer component, and said burning rate catalyst.Another object of this invention is to provide an improved gasgeneration system. Still another object of this invention is to providean improved method of developing thrust which comprises burning saidimproved propellant in the combustion chamber of a rocket motor. Otheraspects, objects and advantages of the invention will be apparent tothose skilled in the art in view of this disclosure.

Thus according to the invention, there is provided as a burning ratecatalyst for solid propellant compositions, a complex of a pyridinecontaining copper and hexavalent chromium, selected from the group ofcompounds characterized by the formula wherein: R is selected from thegroup consisting of alkyl and alkenyl radicals containing from one tofour carbon atoms; R is a pyridyl radical; m is the number of Rsubstituents and can be one of O and 1; n is the number of Rsubstituents and can be one of 0, l, 2 and 3; and the number of pyridinerings within the bracket is always 4, i.e., when m 0 there arev fourpyridine rings as shown, and when m 1 there are two di-pyridyl groups.

Instead of the single structural formula given above, the group ofcompounds forming the burning rate catalysts of the invention can becharacterized by the following structural formulas R R I I R I! Cu Cl201Cu CrzOz I II wherein: in formula I, each R is selected from the groupconsisting of a hydrogen atom and alkyl and alkenyl radicals containingfrom one to four carbon atoms, and at least two of said R substituentsare hydrogen; and wherein: in formula II, each R" is selected from thegroup consisting of a hydrogenatom, a pyridyl radical, and alkyl andalkenyl radicals containing from one to four carbon atoms, one and onlyone of said R substituents is a pyridyl radical, and at least two ofsaid R" substituents are hydrogen.

The compounds characterized by formula I are a presently preferred groupdue to their ease of preparation and availability.

Further according to the invention, there is provided an improved solidpropellant composition comprising a binder component, an oxidizercomponent, and a burning rate catalyst of the type described above.

Still further according to the invention, there is provided an improvedmethod of developing thrust which comprises burning the improvedpropellant of the invention in a combustion chamber of a rocket motor.

Examples of said complex compounds of pyridines which can be used in thepractice of the invention include, among others, the following:

Tetrapyridine copper Il dichromate Tetra-( Z-methylpyridine) copper IIdichromate Tetra-(2,6-dimethylpyridine) copper II dichromateTetra-(2-alpha-methylvinylpyridine) copper II dichromate Tetra-(2-methyl-5-vinylpyridine) copper II dichromate Tetra-(3-butenylpyridine)copper II dichromate Tetra-(3,4,6-trimethylpyridine) copper IIdichromate Tetra-( 3-n-butylpyridine) copper II dichromate Tetra-(2-n-propylpyridine) copper II dichromate Di-(2-( 2-pyridyl)pyridine)copper II dichromate Di-(3-(3-pyridyl)pyridine) copper II dichromateDi-(4-(4-pyridyl)pyridine) copper ll dichromateDi-(2-(2-pyridyl)-4-methylpyridine) copper Il dichromateDi-(2-(2pyridyl)-5-ethylpyridine) copper ll dichromate The amount of theburning rate catalysts employed in the propellant compositions of theinvention is usually within the range of about 0.25 to about 12 parts byweight per 100 parts by weight of base propellant. When calculated onthe basis of the total propellant composition, the amount of saidburning rate catalyst is within the range of about 0.2 to about llweight per cent of said total propellant composition- As used herein andin the claims, unless otherwise specified, the term base propellant" isdefined as binder plus oxidizer.

The presently preferred burning rate catalyst of the invention istetrapyridine copper II dichromate. This material was prepared asfollows. Fifty grams of Cu- SO .5H O was dissolved in 300 grams ofwater. Pyridine was then added in excess to the resulting solution, withstirring, to form a complex with the cupric sulfate. An aqueous solutionof potassium dichromate weight per cent) was then added at roomtemperature to the solution of copper sulfate-pyridine complex. Ayellow-green, fine precipitate of tetrapyridine copper II dichromateimmediately formed. Said precipitate was filtered off, washed withwater, and air dried. This method of preparation can be used inpreparing other burning rate catalysts of the invention, i.e., thehydrocarbon substituted and the pyridyl substituted derivatives oftetrapyridine copper ll dichromate.

The burning rate catalysts of the invention are particularly suitablefor use in propellant compositions wherein the binder componentcomprises a rubbery material, e.g., a natural rubber or a syntheticrubber. Said burning rate catalysts impart an enhanced burning ratehigher than obtained with catalysts of the prior art and do not injurethe physical properties of the propellant.

Oxidizers which are applicable in the solid propellant compositions ofthis invention are those oxygencontaining solids which readily give upoxygen and include, for example, ammonium, alkali metal, and alkalineearth metal salts of nitric, perchloric, and chloric acids, and mixturesthereof. Ammonium nitrate and ammonium perchlorate are the preferredoxidizers for use in the solid propellants of this invention. Otherspecific oxidizers include sodium nitrate, potassium perchlorate,lithium chlorate, calcium nitrate, barium perchlorate, and strontiumchlorate. Mixtures of oxidizers are also applicable. In the preparationof the solid rocket propellant compositions, the oxidizers are ground toa particle size, preferably within the range between 10 and 200 micronsaverage particle size. The amount of solid oxidizer used is usually amajor amount of the total propellant composition and is generally in therange between 50 and 95 per cent by weight of the total propellantcomposition.

It is also within the scope of the invention to include various finelydivided high energy additives in the propellant compositions of theinvention. Examples of said high energy additives include, among others,the following: boron, magnesium, aluminum, lithium, beryllium, variousmetal hydrides, etc. The amount of said high energy additive willusually be within the range of 0 to 15 weight per cent of the totalpropellant compositron.

When the propellant grains are to be prepared by casting techniques,using a liquid binder which is subsequently cured to a solid, the totalsolids content, i.e., solids such as inorganic oxidizing salt, finelydivided high energy additive, burning rate catalyst, etc., should notexceed about weight per cent of the total propellant composition inorder to obtain a flowable mixture which will properly fill the mold inwhich the propellant is cast. In such compositions, the binder contentis increased accordingly.

A class of binder components widely used in solid propellantcompositions and which form a presently preferred class of binders foruse according to the invention comprises a rubbery copolymer of aconjugated diene and a heterocyclic nitrogen base. These copolymers canvary in consistency from liquid polymers having a viscosity as low as300 poises at 25 C., through very soft rubbers, i.e., materials whichare soft at room temperature but will show retraction when relaxed, tothose having a Mooney value (ML-4) up to 100. The solid rubberycopolymers most frequently preferred have Mooney values in the rangebetween 10 and 40. The liquid copolymers most frequently preferred haveviscosities within the range of 300 to 1,000 poises at 25 C. Saidcopolymers can be prepared by any polymerization methods known to theart, e.g., mass or emulsion polymerization. One convenient method forpreparing these copolymers is by emulsion polymerization at temperaturesin the range between 0 and F. Recipes such as the ironpyrophosphatehydroperoxide, either sugar-free or containing sugar, thesulfoxylate, and the persulfate recipes are among those which areapplicable. It is advantageous to polymerize to high conversion as theunreacted vinylpyridine monomer is difficult to remove by stripping.

The conjugated dienes employed are those containing from 4 to 10 carbonatoms per molecule and include 1,3-butadiene, isoprene, 2-methyl-l,3-butadiene, and the like. Various alkoxy, such as methoxy and ethoxyand cyano derivatives of these conjugated dienes, are also applicable.Thus, other dienes, such as phenylbutadiene, 2,3-dimethyl-l,3-hexadiene,2-methoxy-3- ethylbutadiene, 2-ethoxy-3-ethyl-l,3-hexadiene, 2-cyano-1,3-butadiene, are also applicable. Instead of using a singleconjugated diene, a mixture of conjugated dienes can be employed. Thus,a mixture of 1,3- butadiene and isoprene can be employed as theconjugated diene portion of the monomer system.

The polymerizable heterocyclic nitrogen bases which are applicable forthe production of said polymeric materials are those of the pyridine,quinoline, and isoquinoline series which are copolymerizable with aconjugated diene and contain one, and only one,

substituent wherein- R is either hydrogen or a methyl group. That is,the substituent is either a vinyl or an alpha-methylvinyl (isopropenyl)group. Of these, the compounds of the pyridine series are of thegreatest interest commercially at present. Various substitutedderivatives are also applicable but the total number of carbon atoms inthe groups attached to the carbon atoms of the heterocyclic nucleusshould not be greater than because the polymerization rate decreasessomewhat with increasing size of the alkyl group. Compounds where thealkyl substituents are methyl and/or ethyl are available commercially.

These heterocyclic nitrogen bases have the formula where R is selectedfrom the group consisting of hydrogen, alkyl, vinyl, alpha-methylvinyl,alkoxy, halo, hydroxy, cyano, aryloxy, aryl, and combinations of thesegroups such as haloalkyl, alkylaryl, hydroxyaryl, and

- the like; one and only one of said groups being selectedalpha-methylvinyl)-8-dodecylquinoline; 3- vinylisoquinoline;l,G-dimethyl-3-vinylisoquinoline; 2-vinyl-4-benzylquinoline; 3-vinyl-5-chloroethylquinoline-3-vinyl5 ,-dichloroisoquinoline;2-vinyl-6-ethoxy-7-methylquinoline; 3-vinyl-6-hydroxymethylisoquinoline; and the like.

It is often desirable to incorporate carbon black in the copolymerduring its preparation, this addition being accomplished by conventionalmethods, as for example, adding the carbon black to the latex prior tocoagulation. The amount of carbon black can be from zero to 35 parts ofblack per 100 parts of copolymer. In the preparation of the copolymers,the amount of the conjugated diene will be at least 50 parts by weightper 100 parts of the monomer mixture, while the comonomer will be in therange of five to 50 parts. Although, polymerizable heterocyclic nitrogenbases are the preferred comonomers, other comonomers such as styrene areapplicable.

Any of the above-described copolymers can be employed in the practice ofmy invention. In addition, many plastic, resinous, and other rubbery orflexible materials are suitable binder materials for the propellants ofmy invention. Thus, the invention is not to be limited to any particularbinder. Any suitable binder material can be employed. The bindermaterial, per se, forms no part of the invention. Examples of othersuit- 2-vinylquinoline,

able binders can be grouped as follows: asphalt and pitches includingnatural asphalts having a 170 F. softening point, air blown asphaltshaving a 270 F. softening point, mixtures of asphalt and synthetic ornatural rubber, pitch having a 240 F. softening point, and mixtures ofpitch and rubber; epoxy resins, such as Araldite 502 (an epoxy resinprepared by the condensation of epichlorohydrin with bisphenol A asdescribed further in Kirk-Othmer, Encyclopedia of Chemical Technology,Volume X, page 809) and Epon 834 (a synethtic resin possessing terminalepoxide groups as described on page 72 in Zimmerman and Lavine,Supplement I (1956) to the 1953 edition of Handbook of Material TradeNames and in Kirk-Othmer Encyclopedia of Chemical Technology, Volume X,page 809) liquid polymers such as polybutadiene, polybutene,polyisobutylene, and Thiokol LP-3 (one of a series of liquid polysulfidepolymers having a molecular weight of about 1,000 and a viscosity ofabout poises at 25 C. as described on page 241 of Supplementl (1956) tothe 1953 edition of Handbook of Material Trade Names and in Kirk-OthmerEncyclopedia of Chemical Technology, Volume XI, page 842);polyethylenes, rubbers, both natural and synthetic, such as butylrubber, ethyl acrylate-methylvinylpyridine copolymers, polybutadiene,and hydrogenated polybutadiene; waxes, both natural and synthetic havinga melting point within the range of to 300 F.; synthetic resins andplastics such as the various acrylic and polyvinyl resins; and nitropolymers such as polynitromethylmethylacrylate, nitropolybutadiene andpolynitrovinyl alcohols.

The binder frequently will contain various conventional compoundingingredients such as reinforcing agents, plasticizers, wetting agents,anti-oxidants, etc. Other ingredients which are employed for sulfurvulcanization include a vulcanization accelerator, a vulcanizing agentsuch as sulfur, and an accelerator activator, such as zinc oxide. Whenthe binder comprises a copolymer comprising a conjugated diene and apolymerizable heterocyclic nitrogen base, it can also be cured by aquaternization reaction by incorporating therein a quaternizing agentand subjecting the resulting mixture to quaternizing conditions oftemperature.

Suitable quaternizing agents include alkyl halides such as methyliodide, methyl bromide; alkylene halides such as methylene iodide,ethylene bromide; substituted alkanes such as chloroform, brornoform,alkyl sulfates such as methyl sulfate; and various substituted aromaticcompounds such as benzoyl chloride, methyl benzene sulfonate, and thelike. When liquid copolymers are used to form castable binders, thequaternizing agent must be polyfunctional. Examples of such quaternizingagents are: alpha, alpha-dichloro-pxylene; ricinoleyldi-alpha-chloroacetate plus Nacconate 3 l0 (3 ,3 -dimethyl-4,4'-dicyanatodiphenylmethane); and 1,5-dibromopentane. The quaternizingtemperature is usually in the range zero to C., although temperaturesoutside this range can be used. Thus, it will be understood that hereinand in the claims, unless otherwise specified, the term binder isemployed generically and includes various conventional compoundingingredients. The binder content of the propellant composition willusually range from five to 50 per cent by weight.

The various ingredients in the propellant composition can be mixed on aroll mill or an internal mixer such as a Banbury or a Baker-Perkinsdispersion blade mixer can be employed. The binder forms a continuousphase in the propellant with the oxidant as the discontinuous phase. Oneprocedure for blending the propellant ingredients utilizes a stepwiseaddition of the solid ingredients such as oxidizer and burning ratecatalyst to the binder. The binder ingredients are mixed together toform a binder mixture and the oxidizer, burning rate catalyst, etc., arethen added to said binder mixture in substantially equal subsequentadditions. Another suitable mixing procedure is that described inExample I below. Actually, any suitable mixing procedure can be employedand the mixing procedure can be varied depending upon whether the rocketgrains are to be formed by compression molding, injection molding,extrusion, or casting techniques.

After the grains are formed, they are cured. The curing temperature willbe limited by the oxidizer employed in some cases but will generally bein the range between 70 and 250 F., preferably between 170 and 200 F.The curing time must be long enough to give required creep resistanceand other mechanical properties in the propellant. The time willgenerally range from around three hours when the higher curingtemperatures are employed to seven days when curing is effected at lowertemperatures.

The following examples will serve to further illustrate the invention.

EXAMPLE Five propellants having the compositions given in Table I belowwere prepared.

In preparing propellant A, the solids (ammonium perchlorate, aluminumpowder, and tetrapyridine copper II dichromate) were blended together ina 35 cubic inch Z-blade mixer for a period of 1 minute. The liquids(Bd/MVP, ZP-21l, HDMPCA, RCA, and Kel F Oil) were then added to saidsolids and blended for 15 minutes at 160 F. Nacconate 310 (also aliquid) was then added to the resulting blend and mixing was continued,this time under vacuum, for an additional period of minutes at 160 F.The final mixture was poured into strand molds, the molds were vibratedfor 1 hour to remove entrained gases, and the resulting strands werecured for 48 hours at 160 F.

In preparing propellant B, the solids (ammonium perchlorate, aluminumpowder, and tetrapyridine copper II dichromate) were blended togetherfor 1 minute as in the preparation of propellant A. The liquids (Bd-MVP, ZP-2l l, and Kel F Oil) were then added to the blend of solids andthe mixture blended for an additional minutes at 160 F. The alpha,alpha,- dichloro-para-xylene was then added to the blend and mixingcontinued, this time under vacuum, for 10 minutes at 160 F. The finalmixture was poured into strand molds, the molds were vibrated for 1 hourto remove entrained gases, and the resulting strands were then cured for48 hours at 160 F.

In preparing propellant C, the catalyst tetrapyridine copper IIdichromate was omitted. Otherwise, the method of preparation given abovefor propellant A was followed.

In preparing propellant D, the catalyst tetrapyridine copper IIdichromate was omitted. Otherwise, the method of preparation given abovefor propellant B was followed.

In preparing propellant E, a conventional catalyst, copper chromite, wasemployed instead of tetrapyridine cupric dichromate. Otherwise, themethod of preparation given above for propellant A was followed.

5 TABLE I.COMPOSITION 0F PROPELLANTS Propellant, weight percentIngredients A MMB- C l) E Liquid Bd/MVP (75/25) 13. 02 13.37 13. 02 13.37 13. 02 10 ZP-Zll. 1. 96 4. 69 1. 96 4. 69 1. 06

HDMPCA 1.05 RCA 1. 57 Naceonate 310 1. 40 R211 polymer oil No.3 1.00Ammonium perchlorate (18 micron particle size)....... 11. 70 11.70 1 0012. 0U 11. TU Ammonium perchlorate (200 micron particle size) 54.1105-1. (30 56. 00 56. ()0 54. 60 Aluminum powder (13 mircon). 11. 11.7012.00 12. 00 11.70 Tetrapyridine cooper II (lichr0n1ate.... 7 J. 00 2.00 Copper chromite. 2. on

Total 100. 00 100. 01) 100. 00 100. ()0 I00. [)0

The burning rate was obtained upon samples of the above-describedpropellant compositions A, B, C, D and E by burning strands of each in aCrawford bomb in the usual manner. Briefly, this method comprisesrestricting a strand of the propellant to be tested on all surfacesexcept one end so as to prevent burning except on said end. Said strandis then placed in a pressure bomb in a temperature bath maintained at aconstant temperature (usually 70 F.), and the bomb is pressured to thedesired pressure with nitrogen. Said strand is then ignited and the timerequired for the propellant to burn between two fusible wires spaced aknown distance apart is recorded. The burning rate is then calculated ininches per second. The results of burning rate tests on theabove-described propellant compositions are given in Table II below.

TABLE II Burning Rates of Propellants a From test results. b From plotof test results A comparison of the burning rates at 1,000 psi forpropellants A and C shows that the tetrapyridine copper Il dichromatecatalyst materially increased .the burning rate of propellant A overthat of propellant B which contained no catalyst.

A comparison of the burning rates at 1000 psi for propellants B and Dshows that the tetrapyridine copper II dichromate catalyst materiallyincreased the burning rate of propellant B over that of propellant Dwhich contained no catalyst.

A comparison of the burning rates at 1000 psi for propellants A, C, andB shows that the tetrapyridine copper II dichromate catalyst ofpropellant A is a more effective catalyst than the copper chromitecatalyst of propellant B.

As will be evident to those skilled in the art, various modifications ofthe invention can be made, or followed, in the light of the abovedisclosure without departing from the spirit or scope of said invention.

I claim:

1. An improved solid composite type propellant composition comprising:as a base propellant, a major amount of a solid'inorganic oxidizing saltas an oxidizer component and a minor amount of a suitable bindercomponent comprised of a material selected from the group consisting ofnatural rubber, synthetic rubber, copolymers of a conjugated dienecontaining from four to 10 carbon atoms per'molecule with apolymerizable heterocyclic nitrogen base, copolymers of a conjugateddiene containing from four to 10 carbon atoms per molecule with styrene,asphalt, pitch, mixtures of asphalt and natural rubber, mixtures ofasphalt and synthetic rubber, mixtures of pitch and natural rubber,mixtures of pitch and synthetic rubber, epoxy resins, polybutadiene,polybutene, polyisobutylene, hydrogenated polybutadiene, natural waxes,synthetic waxes, polyethylenes, polysulfide rubbers, acrylic resins,polyvinyl resins, and nitro polymers; and from about 0.25 to about 12parts by weight per 100 parts by weight of said base propellant of aburning rate catalyst consisting essentially of a complex of a pyridinecontaining copper and hexavalent chromium and selected from the group ofcompounds characterized by the formula Crz01 n is the number of Rsubstituents and is an integer of from 0 to 3.

2. A propellant composition according to claim 1 wherein said burningrate catalyst is tetrapyridine copper II dichromate.

3. A propellant composition according to claim 1 wherein said burningrate catalyst is tetra-(2- methylpyridine) copper ll dichromate.

4. A propellant composition according to claim 1 wherein said burningrate catalyst is tetra-(2,6- dimethylpyridine) copper ll dichromate.

5. A propellant composition according to claim 1 wherein said burningrate catalyst is tetra-(Z-methyl-S- vinylpyridine) copper ll dichromate.

6. A propellant composition according to claim 1 wherein said burningrate catalyst is tetra-(3,4,6- trimethylpyridine) copper II dichromate.

7. A propellant composition according to claim 1 wherein said burningrate catalyst is di-(2-(2- 10 pyridyl)pyridine) copper II dichromate.

8. A propellant composition according to claim 1 wherein said burningrate catalyst is di-(3-(3- pyridyl)pyridine) copper II dichromate.

9. A propellant composition according to claim 1 wherein said burningrate catalyst is di-(4-(4- pyridyl)pyridine) copper II dichromate.

10. In the method of developing thrust wherein a solid propellant chargecontained in a combustion chamber of a rocket motor is ignited and thenburned with the evolution of combustion gases which are exhausted fromsaid combustion chamber, the step which comprises burning in saidcombustion chamber a propellant charge comprising: as a base propellant,a major amount of a solid inorganic oxidizing salt as an oxidizercomponent and a minor amount of a suitable binder component comprised ofa material selected from the group consisting of natural rubber,synthetic rubber, copolymers of a conjugated diene containing from fourto 10 carbon atoms per molecule with a polymerizable heterocyclicnitrogen base, copolymers of a conjugated diene containing from four to10 carbon atoms per molecule with styrene, asphalt, pitch, mixtures ofasphalt and natural rubber, mixtures of asphalt and synthetic rubber,mixtures of pitch and natural rubber, mixtures of pitch and syntheticrubber, epoxy resins, polybutadiene, polybutene, polyisobutylene,hydrogenated polybutadiene, natural waxes, synthetic waxes,polyethylenes, polysulfide rubbers, acrylic resins, polyvinyl resins,and nitro polymers; and from about 0.25 to about 12 parts by weight perparts by weight of said base propellant of a burning rate catalystconsisting essentially of a complex of a pyridine containing copper andhexavalent chromium and selected from the group of compoundscharacterized by the formula n OM07 of R substituents and is an integerof from 0 to 1; and n is the number of R substituents and is an integerof from 0 to 3.

11. A method according to claim 10 wherein said burning rate catalyst istetrapyridine copper II dichromate.

12. A method according to claim 10 wherein said burning rate catalyst istetra-(2-methylpyridine) copper ll dichromate.

13. A method according to claim 10 wherein said burning rate catalyst istetra-(2,6-dimethylpyridine) copper ll dichromate.

14. A method according to claim 10 wherein said burning rate catalyst istetra-(2-methyl-5- vinylpyridine) copper II dichromate. 7

15. A method according to claim 10 wherein said burning rate catalyst istetra-(3,4,6-trimethylpyridine) copper ll dichromate.

16. A method according to claim 10 wherein said burning rate catalyst isdi(2-(2-pyridyl)pyridine) copper ll dichromate.

- 17. A method according to claim 10 wherein said burning rate catalystis di(3-(3-pyridyl)pyridine) copper ll dichromate.

18. A method according to claim 10 wherein said burning rate catalyst isdi-(4-(4-pyridyl)pyridine) copper ll dichromate.

1. AN IMPROVED SOLID COMPOSITE TYPE PROPELLANT COMPOSITION COMPRISING: AS A BASE PROPELLANT, A MAJOR AMOUNT OF A SOLID INORGANIC OXIDIZING SALT AS AN OXIDIZER COMPONENT AND A MINOR AMOUNT OF A SUITABLE BINDER COMPONENT COMPRISED OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF NATURAL RUBBER, SYNTHETIC RUBBER, COPOLYMERS OF A CONJUGATED DIENE CONTAINING FROM 4 TO 10 CARBON ATOMS PER MOLECULE WITH A POLYMERIZABLE HETEROCYCLIC NITROGEN BASE, COPOLYMERS OF A CONJUGATED DIENE CONTAINING FROM 4 TO 10 CARBON ATOMS PER MOLECULE WITH STRYRENE ASPHALT, PITCH, MIXTURES OF ASPHALT AND NATURAL RUBBER, MIXTURES OF ASPHALT AND SYNTHETIC RUBBER, MIXTURES OF PITCH AND NATURAL RUBBER, MIXTURES OF PITCH AND SYNTHETIC RUBBER, EPOXY RESINS, POLYBUTADIENE, POLYBUTENE, POLYISOBUTYLENE, HYDROGENATED POLYBUTADIENE, NATURAL WAXES, SYNTHETIC WAXES, POLYETHYLENES, POLYSULFIDE RUBBERS, ARCYLIC RESINS, POLYVINYL RESINS, AND NITRO POLYMERS; AND FROM ABOUT 0.25 TO ABOUT 12 PARTS BY WEIGHT PER 100 PARTS BY WEIGHT OF SAID BASE PROPELLANT OF A BURNING RATE CATALYST CONSISTING ESSENTIALLY OF A COMPLEX OF A PYRIDINE CONTAINING COPPER AND HEXAVALENT CHROMIUM AND SELECTED FROM THE GROUP OF COMPOUNDS CHARACTERIZED BY THE FORMULA
 2. A propellant composition according to claim 1 wherein said burning rate catalyst is tetrapyridine copper II dichromate.
 3. A propellant composition according to claim 1 wherein said burning rate catalyst is tetra-(2-methylpyridine) copper II dichromate.
 4. A propellant composition according to claim 1 wherein said burning rate catalyst is tetra-(2,6-dimethylpyridine) copper II dichromate.
 5. A propellant composition according to claim 1 wherein said burning rate catalyst is tetra-(2-methyl-5-vinylpyridine) copper II dichromate.
 6. A propellant composition according to claim 1 wherein said burning rate catalyst is tetra-(3,4,6-trimethylpyridine) copper II dichromate.
 7. A propellant composition according to claim 1 wherein said burning rate catalyst is di-(2-(2-pyridyl)pyridine) copper II dichromate.
 8. A propellant composition according to claim 1 wherein said burning rate catalyst is di-(3-(3-pyridyl)pyridine) copper II dichromate.
 9. A propellant composition according to claim 1 wherein said burning rate catalyst is di-(4-(4-pyridyl)pyridine) copPer II dichromate.
 10. In the method of developing thrust wherein a solid propellant charge contained in a combustion chamber of a rocket motor is ignited and then burned with the evolution of combustion gases which are exhausted from said combustion chamber, the step which comprises burning in said combustion chamber a propellant charge comprising: as a base propellant, a major amount of a solid inorganic oxidizing salt as an oxidizer component and a minor amount of a suitable binder component comprised of a material selected from the group consisting of natural rubber, synthetic rubber, copolymers of a conjugated diene containing from four to 10 carbon atoms per molecule with a polymerizable heterocyclic nitrogen base, copolymers of a conjugated diene containing from four to 10 carbon atoms per molecule with styrene, asphalt, pitch, mixtures of asphalt and natural rubber, mixtures of asphalt and synthetic rubber, mixtures of pitch and natural rubber, mixtures of pitch and synthetic rubber, epoxy resins, polybutadiene, polybutene, polyisobutylene, hydrogenated polybutadiene, natural waxes, synthetic waxes, polyethylenes, polysulfide rubbers, acrylic resins, polyvinyl resins, and nitro polymers; and from about 0.25 to about 12 parts by weight per 100 parts by weight of said base propellant of a burning rate catalyst consisting essentially of a complex of a pyridine containing copper and hexavalent chromium and selected from the group of compounds characterized by the formula
 11. A method according to claim 10 wherein said burning rate catalyst is tetrapyridine copper II dichromate.
 12. A method according to claim 10 wherein said burning rate catalyst is tetra-(2-methylpyridine) copper II dichromate.
 13. A method according to claim 10 wherein said burning rate catalyst is tetra-(2,6-dimethylpyridine) copper II dichromate.
 14. A method according to claim 10 wherein said burning rate catalyst is tetra-(2-methyl-5-vinylpyridine) copper II dichromate.
 15. A method according to claim 10 wherein said burning rate catalyst is tetra-(3,4,6-trimethylpyridine) copper II dichromate.
 16. A method according to claim 10 wherein said burning rate catalyst is di(2-(2-pyridyl)pyridine) copper II dichromate.
 17. A method according to claim 10 wherein said burning rate catalyst is di(3-(3-pyridyl)pyridine) copper II dichromate.
 18. A method according to claim 10 wherein said burning rate catalyst is di-(4-(4-pyridyl)pyridine) copper II dichromate. 